U.S. Pat. No. 3,036,971 discloses preparing detergent dispersant additives based on sulfurized alkylphenates of high basicity alkaline earth metals. These additives are prepared by sulfurization of an alkylphenol, neutralization of the sulfurized alkylphenol with an alkaline earth base, then super-alkalization by carbonation of the alkaline earth base dispersed in the sulfurized alkylphenate. French patent 1,563,557 discloses detergent additives based on sulfurized calcium alkylsalicylates. These additives are prepared by carboxylation of a potassium alkylphenate, exchange with calcium chloride, then sulfurization of the calcium alkylsalicylate obtained with sulfur in the presence of lime, a carboxylic acid and an alkylene glycol or alkyl ether of alkylene glycol.
Applicants' French patent application 2,625,220 discloses superalkalized detergent-dispersant additives based on alkylphenates and alkylsalicylates. These additives are prepared by neutralization of an alkylphenol with an alkaline earth base in the presence of an acid and a solvent, distillation of the solvent, carboxylation, sulfurization and superalkalization by sulfur and an alkaline earth base in the presence of glycol and solvent, followed by carbonation and filtration.
Applicants' PCT patent application PCT/FR95/00299 discloses a process that is able to improve substantially the performance of these additives, particularly in the tests relating to foaming, compatibility and dispersion in a new oil, and in the tests of stability towards hydrolysis. This process comprises neutralization with alkaline earth base of a mixture of linear and branched alkylphenols in the presence of a carboxylic acid, carboxylation by the action of carbon dioxide of the alkylphenate, followed by sulfurization and superalkalization, then carbonation, distillation, filtration, and degassing in air.